1. Field of the Invention
The present invention relates to a printed wiring board, an information processing apparatus provided with this printed wiring board, and a method of manufacturing the printed wiring board.
2. Description of the Related Art
In recent years, printed wiring boards to mount densely integrated semiconductor devices such as hybrid ICs, MCMs (Multi Chip Modules), and the like have been made denser using a greater number of layers or finer patterns and have greatly contributed to the reduction in size and weight of electronic equipment as densely packed circuit boards in electronic parts.
In such a printed wiring board designed to be so dense, in order to ensure connection reliability, a technology to restrain cracking or the like in the wiring pattern due to stress or the like added from outside by a structure in which the excurrent direction of prepreg fiber (direction of fiber) used as an insulating layer is slanted, for instance, by 45 degrees with respect to a side of the substrate body, is proposed (for instance, Patent Document 1).
[Patent Document 1] Japanese translated application of PCT International Application (P2002-501676=JP-A 2003-535743=WO 01/094134 A)
However, in the case of the printed wiring board described in the above-document, since a rectangular shape of the printed wiring board needs to be cut down and hauled out from a parent material being an insulating layer in a state having an angle with respect to the direction of fiber, much of the parent material is left as scrap, which poses a problem in terms of manufacturing costs.
On the other hand, when a printed wiring board which obtains an insulating layer from prepreg and the like is used as a controlling board which requires high speed data transmission, the following problem becomes apparent: the transmission characteristics of the signals carried by wiring patterns deteriorate in a printed wiring board having a ground layer and a plurality of wiring patterns for signal transmission positioned facing to the ground layer while sandwiching a fiber-containing insulating layer.
Concretely, a wiring pattern wired right above the fibers along the direction of fiber in the insulating layer and a wiring pattern wired at a position away from right above the fibers differ in capacitance created between their respective ground layers (thickness direction of the substrate). Accordingly, impedance in the extending direction of the wiring pattern (transmitting direction of signal) differs between the former wiring pattern and the latter wiring pattern, which creates differences in signal transmission speed or signal noise. These phenomena become more apparent as the signal transmission speed increases.